This invention relates to a process for reducing the weight average molecular weight (Mw) and the melt index ratio (MIR) of ethylene homopolymers, interpolymers, and functionalized ethylene homopolymers and interpolymers. The process includes subjecting a polymer, in molten form, to specified conditions of temperature, stirring and residence time in multiple reaction zones such that the resultant polymeric product is characterized by having reduced weight average molecular weight (Mw) and reduced melt index ratio (MIR) values, as compared to the starting polymer. The invention also relates to novel ethylene homopolymers, interpolymers, and functionalized ethylene polymers and interpolymers, that are useful in many applications, such as, for example, in blown film, cast film, extrusion coating, injection molding, adhesive and sealant raw materials, and the like.
U.S. Pat. No. 5,631,346 describes a process for degrading polyolefins in a twin-screw extruder operated a pressure of 1-100 bar, wherein the pressure is changed with a range of variation of 0.5-30 bar.
British Patent No. 1,042,178 describes narrowing the molecular weight distribution of polyolefins by degradation using high shear gradients at temperatures between the melting point and the temperature at which purely thermal degradation of the polyolefin occurs.
U.S. Pat. No. 3,087,922 describes a process for the pyrolysis of a high molecular weight polyolefin to produce a lower molecular weight polymer by passing the polymer through a pyrolysis zone in the form of a fluid stream having annular cross section, and transferring heat of pyrolysis to the polymer through both exterior and interior boundaries of the annular stream. U.S. Pat. No. 3,248,469 describes a method of visbreaking a polymer of an olefin by feeding the polymer to a shearing zone at a controlled rate, passing sheared polymer through an extrusion zone, and maintaining a positive back pressure on the polymer. U.S. Pat. No. 5,292,862 describes a continuous process for the production of low molecular weight polyolefin by feeding the polymer to an extruder for melting, metering the molten polymer at a constant rate to a tubular degradation reactor, and thermally degrading the polymer in the reactor in the presence of a higher fatty acid, a hydrochloric acid acceptor or a mixture thereof.
The following patents describe polyolefin degradation processes that utilize a catalyst. U.S. Pat. No. 3,332,926 describes a process for degrading polyolefins by mixing a crystalline polyolefin with a metal salt of a carboxylic acid and heating the resultant mixture in an atmosphere substantially free of oxygen to a temperature of 275-450xc2x0 C. U.S. Pat. No. 3,345,352 describes a process for degrading polyolefins by heating the polymer to a temperature of 275-450xc2x0 C. in the presence of an oxide or carbonate catalyst and in the absence of oxygen for at least five minutes. U.S. Pat. No. 3,519,609 describes a process for degrading polyolefins at temperatures of 200-400xc2x0 C. in the absence of oxygen and in the presence of an organic anhydride catalyst. U.S. Pat. No. 3,562,788 describes a process for degrading polyolefins in the presence of metal coordination polymerization catalyst residue. U.S. Pat. Nos. 3,723,402 and 3,842,153 describe processes for degrading isotactic polypropylene in the presence of an organosilicon compound.
The following patents describe processes for degrading polyolefins wherein an oxygen-containing gas is utilized. U.S. Pat. Nos. 3,551,943; 3,563,972; and 3,608,001 describe degradation processes utilizing an extruder-reactor to heat mixtures of polypropylene with an oxygencontaining gas, wherein feedback means are provided to change the temperature in the extruder thereby controlling the molecular weight of the exiting polymer. U.S. Pat. No. 3,898,209 describes a process for controlled scission of polypropylene by injection, under pressure, controlled amounts of oxygen into the melt-phase of the polypropylene at specified temperatures. U.S. Pat. No. 3,940,379 describes a process for controlled oxidative degradation of propylene polymers by injecting oxygen or an oxygen-containing gas and an organic or inorganic peroxide, melting and working the resulting mixture in a high shear zone, and recovering an essentially odor-free propylene polymer having a melt flow rate higher than that of the feed polymer.
The following patents describe processes for degrading polyolefins by mixing another polymer therewith. U.S. Pat. No. 3,121,070 describes the degradation of polypropylene at temperatures of 275-450xc2x0 C. in the presence of a modifying polymer. U.S. Pat. No. 3,598,885 describes a process for preparing low molecular weight polymers by mixing relatively thermally stable polyolefins with relatively-thermally unstable polymers and thermally cracking the mixture.
The following patents describe processes for degrading polyolefins wherein a free-radical initiator is utilized. U.S. Pat. No. 4,707,524 describes the degradation of polypropylene by mixing a peroxide therewith and melting the resulting mixture under thermal mechanical action. U.S. Pat. No. 4,749,505 describes a process for degrading polyolefins in the presence of a free-radical initiator, under an inert blanket of nitrogen. U.S. Pat. No. 5,594,074 describes a process wherein unreacted free-radical generators are used to produce polymer pellets that are degraded by thermal treatment. U.S. Pat. Nos. 3,862,265 and 4,001,172 describe processes for degrading polyolefins in extruders wherein free-radical initiators are injected into the reaction zone. U.S. Pat. No. 5,530,073 describes a process for the controlled degradation of polypropylene having increased peroxide efficiency. U.S. Pat. No. 5,587,434 describes a process for degrading polypropylene wherein polypropylene is mixed with a free-radical generator in increments, in an extruder. This is also described in U.S. Pat. No. 3,144,436.
The novel products of the present invention include ethylene interpolymers and functionalized ethylene interpolymers, having a melt index ratio (MIR) of less than 26, a molecular weight distribution (MWD) of greater than 2.4 and a density of less than 0.95 g/cc. Also included as novel products of the present invention are ethylene homopolymers, interpolymers, and functionalized ethylene homopolymers and interpolymers, having a melt index ratio (MIR) of less than 22 and a molecular weight distribution value of greater than 2.4.
The novel process of the present invention for the production of ethylene homopolymers, interpolymers, and functionalized ethylene homopolymers and interpolymers, having reduced weight average molecular weigth (Mw) and reduced melt index ratio (MIR), including the novel ethylene homopolymers, interpolymers, and functionalized ethylene homopolymers and interpolymers, of the present invention, is comprised as follows. An ethylene homopolymer and/or interpolymer is introduced into an apparatus in the form of a solid particulate, for example, pellets or powder, and then melted, preferably at a temperature of at least 175xc2x0 C.; the molten polymer is then introduced into at least two, or more, reaction zone(s)-that are sequentially located and heated to a temperature of at least 220xc2x0 C., more preferably from at least 280xc2x0 C. to about 600xc2x0 C.; when utilized, a functionalizing agent may be introduced into the melting zone or at least one, or more of the reaction zones, or any combinations thereof; subjecting the molten polymer, in the heated zones, to sufficient stirring and residence time such that the molecular weight (Mw) and the melt index ratio (MIR) of the polymer are reduced; and recovering the resultant polymeric product having the reduced molecular weight (Mw) and reduced melt index ratio (MIR). The conditions in each of the reaction zones, into which molten polymer is introduced, may be the same or different. In a preferred embodiment of the process, the apparatus is vented, preferably by means of vacuum venting, subsequent to formation of the desired polymeric product and prior to recovering the polymeric product.
The applicant has unexpectedly discovered a novel process for producing ethylene homopolymers, interpolymers, and functionalized ethylene homopolymers and interpolymers, having reduced weight average molecular weight (Mw) and reduced melt index ratio (MIR), as compared to the starting polymeric material. The process may be used to prepare a wide variety of ethylene homopolymers and/or interpolymers and/or functionalized ethylene homopolymers and interpolymers, having reduced weight average molecular weight (Mw) and melt index ratio (MIR) values, including the novel ethylene homopolymers, interpolymers, and functionalized ethylene homopolymers and interpolymers of the present invention.
The novel ethylene homopolymers, interpolymers, and functionalized ethylene homopolymers and interpolymers, of the present invention include the following products.
A first type of novel product includes ethylene interpolymers, and functionalized ethylene interpolymers, characterized by having a melt index ratio (MIR) value of less than 26, a molecular weight distribution value (Mw/Mn) of greater than 2.4 and a density of less than 0.95 g/cc. The novel ethylene interpolymers, and functionalized ethylene interpolymers, of the present invention are preferably characterized by having a melt index ratio of from 1 to less than 26, a molecular weight distribution of from greater than 2.4 to about 30, and a density of from greater than 0.87 to less than 0.95 g/cc.
Another type of novel product includes ethylene homopolymers, interpolymers, and functionalized ethylene homopolymers and interpolymers, characterized by having a melt index ratio value of less than 22 and a molecular weight distribution value of greater than 2.4. The novel ethylene homopolymers, interpolymers, and functionalized ethylene homopolymers and interpolymers, are preferably characterized by having a melt index ratio value of from 1 to less than 22 and a molecular weight distribution value of from greater than 2.4 to about 30.
Furthermore, with respect to the above described types of novel polymers, the ethylene interpolymers and functionalized ethylene interpolymers are characterized as interpolymers of ethylene with at least one or more other olefin monomer having from 3 to 16 carbon atoms, containing at least 50% by weight of ethylene.
The novel polymeric products are useful in many applications including, for example, blown film, cast film, extrusion coating, injection molding, and the like.
The novel process of the present invention for producing ethylene homopolymers, interpolymers, and functionalized ethylene homopolymers and interpolymers, having reduced melt index ratio and reduced weight average molecular weight (Mw) values comprises:
a. introducing ethylene homopolymer and/or interpolymer in solid particulate form (for example, powder or pellets). into an apparatus and melting the ethylene homopolymer and/or interpolymer at a temperature above the melting point of the polymer, preferably at a temperature of at least 175xc2x0 C.
b. introducing the molten polymeric product into at least two, or more, reaction zones that are sequentially located and are each maintained at a temperature of at least 220xc2x0 C., preferably at a temperature of from about 280xc2x0 C. to about 600xc2x0 C.,
c. when utilized, a functionalizing agent may be introduced into the melting zone or at least one, or more, of the reaction zones, or any combination thereof;
d. subjecting the molten polymeric product, in each of the heated zones, to sufficient stirring and residence time such that the weight average molecular weight.(Mw) and the melt index ratio (MIR) values of the polymeric product are reduced, and
e. recovering the resultant ethylene homopolymer or interpolymer having reduced weight average molecular weight (Mw) and reduced melt index ratio (MIR).
Where it is desired to produce a functionalized ethylene homopolymer and/or interpolymer, a functionalizing agent is introduced into the melting zone or any of the reaction zones, or any combination of melting zone and reaction zones.
In the process of the present invention, the molten polymeric product, in each of the heated zones, is stirred preferably at a rate of from at least about 100 revolutions per minute (rpm), preferably from about 100 to about 1500 rpm, and more preferably at a rate of from about 300 to about 500 revolutions per minute (rpm), for a period of time of at least about 5 seconds, preferably for at least about 5 to 300 seconds, and, more preferably, for a period of time of at least from about 30 to about 120 seconds.
Furthermore, the interpolymers of ethylene that are suitable for use in the process of the present invention are interpolymers of ethylene with at least one other monomer that is interpolymerizable with the ethylene, wherein the ethylene is present in an amount of at least about 50 weight percent. Mixtures of interpolymers of ethylene can be utilized herein. The at least one other monomer may be an olefin having from 3 to 16 carbon atoms. Exemplary olefins that may be utilized herein are propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 4-methylpent-1-end, 1-decene, 1-dodecene, 1-hexadecene and the like. Also utilizable herein are polyenes such as 1,3-hexadiene, 1,4-hexadiene, cyclopentadiene, dicyclopentadiene, 4-vinylcyclohex-1-ene, 1,5-cyclooctadiene, 5-vinyldene-2-norbornene, 5-vinyl-2-norbornene, 1,7 octadiene.
Exemplary of other monomers that are interpolymerizable with ethylene and are suitable for use herein, include alkyl acrylates, where the alkyl group has from about 1 to about 15 carbon atoms, such as methyl acrylate, n-butyl acrylate, n-propyl acrylate, 2-ethylhexyl acrylate, ethyl acrylate, and the like; alkyl methacrylates wherein the alkyl group has from about 1 to about 15 carbon atoms, such as methyl methacrylate, n-butyl methacrylate, n-propyl methacrylate, n-pehtyl methacrylate, 2-ethylhexyl methacrylate, ethyl methacrylate, and the like; ethylenically unsaturated carboxylic acids such as acrylic acid, crotonic acid, methacrylic acid, and the like; ethylenically unsaturated dicarboxylic acids or anhydrides thereof, such as itaconic acid, maleic acid, fumaric acid, maleic anhydride, and the like; vinyl carboxylates where the carboxylates have from about 1 to about 15 carbon atoms, such as vinyl acetate, vinyl propionate, and the like; mixtures of monomers interpolymerizable with ethylene may also be utilized to provide ethylene interpolymers suitable for use herein.
The functionalizing agent utilized in the present invention may be any unsaturated monomer containing one or more carboxylic acid or acid anhydride groups. Examples of suitable functionalizing agents herein are carboxylic acids such as acrylic and methacrylic acid, and acid anhydrides such as maleic anhydride. Further exemplary functionalizing agents suitable for use herein are unsaturated monocarboxylic acids and polycarboxylic acids and cyclic acid anhydrides. Specifically included herein are acids such as maleic acid, fumaric acid, himic acid, itaconic acid, citraconic acid, mesaconic acid, acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, and acid anhydrides such as maleic anhydride and himic anhydride. Preferred for use herein as the functionalizing agent is maleic anhydride. Mixtures of functionalizing agents may be utilized in the present invention. The functionalizing agent is utilized in any amount that will functionalize the ethylene homopolymer and/or interpolymer. Preferably, the functionalizing agent will be utilized in an amount of from about 0.20 to about 10 weight percent, based on the weight of the ethylene component; more preferably in an amount of about 0.50 to about 8 weight percent, and still more preferably in an amount of about 0.50 to about 4 weight percent.
In a preferred embodiment of the process of the present invention, venting of the process is carried out after the desired polymeric product having the reduced molecular weight and reduced melt index ratio has been produced, and prior to recovering the desired polymeric product. It is preferred that the venting be vacuum venting at a pressure less than atmospheric pressure. Venting is performed for the discharge of volatile materials.
The process according to the present invention is conducted in a continuous or batch process. Any continuous process can be used in the practice of the present invention. However, multi-screw extruders are generally more preferred, with a twin-screw extruder being most preferred. In general, the twin-screw extruder has two shafts that are preferably intermeshing, and that may be either co-rotating or counter-rotating. As used herein, the term, intermeshing, describes shafts that fit together such that the shafts rotate in coordination with each other in close proximity without mechanical interference. Further, as used herein, the term, corotating, describes shafts rotating in the same direction; the term, counterrotating, describes shafts rotating in opposite directions.